1. Field of the Invention:
The present invention relates to an automatic strapping machine for winding a package with a thermoplastic band (hereinafter referring to as a band) and tightening the band and melt-sealing a superposed part of the band by heating under pressure and cutting the band from the feeding side adjacent to the melt-sealed part.
2. Description of the Prior Art
Various structures of the automatic strapping machine have been proposed and the fields of the applications have been rapidly broaden and various kinds of the machines have been provided depending upon size of a package, hardness, softness and compressability.
From the viewpoints of the saving of petrochemical products and articles of consumption, narrow width of band has been used whereby it has been important to maintain the parallel condition of the superposed part of the bands in the heat-sealing operation.
In a conventional automatic strapping machine, a band contacted along the peripheral part of a band feeding roller is fed into an arch under contacting with a free roller and the leading end of the band is passed through the arch is gripped with a first gripper having a cutter for cutting the band, the band feeding roller is reversely rotated to tighten the package, the end of the band is gripped by a second gripper, a heating element is inserted between the superposed part of the bands gripped by the first and second grippers without tension, the two upper and lower bands and the heating element are pressed between a cutter anvil, a pressing element and the band is cut by a cutter fixed on the side surface of the pressing element and an edge of the first gripper, the bands and the heating element are pressed to melt the surfaces of the bands contacted with the heating element and the heating element is removed to press the bands under cooling so as to heat-seal the superposed part of the band.
In the machine as disclosed in the Japanese Utility Model Publication No. 23280/1965, the package is tightened with the band by a roller which is disposed beside the band feeding roller and is always reversely rotating at high speed, and is further tightened with a tension lever in high tension when the package is wound with the band.
In these conventional machines, the following disadvantages have been found.
(1) The superposed part of the bands is heat-melted in the condition of no tension and then the heating element is removed, whereby sometimes, the band is slipped out with the movement of the heating element. Also band itself has curl whereby sometimes the superposed part of the bands is not kept in precisely parallel, and the non-parallel superposed part is sealed. Where a narrow band has been used, the disadvantageous effect is often found of a decrease in sealing strength. The present invention serves to completely overcome the disadvantageous of slip of the superposed part of the bands and to bind a package having small width.
(2) When one feed roller is forwardly and reversely rotated to attain the feeding of the band and the tightening of the package, it has been difficult to attain high speed operation because of the time-consuming switching. In order to attain proper operation, motor and transmitting parts need be increased. For example, a long length for tightening is needed to bind a compressive blanket whereas only a short length for tightening is needed to bind a wooden box. In order to tighten both of them under 60 kg of tension, the large motor and transmitting parts are needed. The present invention serves to provide a strapping machine having simple structure with a small motor.
(3) The field of the application of strapping machines have been broadened so as to sometimes be used in an environment of floating fine dust for causing wear in the sliding parts of the machine such as bricks and roof plates in a ceramics factory. In these cases, the life of the cutter is shortened. An expensive cutter made of highly quality material is dulled for short time. It is clear from our experience that a thin paper or cloth is easily cut under tension with scissors even though being dull. When the band has been cut under no tension as with a conventional machine, the band is not easily cut and a cutter made of high quality material has been needed such that the life of the cutter has been short.
The invention serves to provide a machine for easily cutting the band for long life under suitable tension.